A PLANAR UNIMORPH-BASED ACTUATOR WITH LARGE VERTICAL DISPLACEMENT CAPABILITY - PART II - THEORY

A piezoelectric actuator utilizing a planar trellis-like arrangement o f multiple unimorph elements is described which produces displacements perpendicular to the plane of the actuator. The unimorph elements are connected in series mechanically so that the vertical displacement of each unimorph element in the structure adds to the vertical displacem ents of the other elements, resulting in a large overall vertical disp lacement at the output of the actuator. A simple electromechanical mod el of the actuator is developed. The model consists of a voltage-actua ted force source, which is the result of the piezoelectric properties of the unimorph bars that make up the actuator, in parallel mechanical ly with a stiff spring that models the elastic response, both bending and twisting, of the unimorph elements. The long moment arms inherent in the geometry of the actuator make a substantial contribution to the overall compliance of the actuator. The addition of stiffeners to the actuator can significantly reduce the effect of these moment arms, an d thus substantially increase the stiffness of the actuator. As a resu lt, the force generation capability of the actuator is significantly i ncreased without affecting its displacement capability.